# Homework Help: Electric field inside the bulb !

1. May 26, 2008

### luckyducky

Electric field inside the bulb!!!!!!

There are 6.3e28 mobile electrons per cubic meter in tungsten. The cross-sectional area of the tungsten filament in bulb B1 is 0.01 mm2 (1 mm2 = 1e-6 m^2). The electron mobility in hot tungsten is 1.2e-4 (m/s)/(N/C). Calculate the magnitude of the electric field inside the tungsten filament in bulb

2. Relevant equations

E= electric field
V= voltage
L = length of the filament
E = (V/L)

V= IR v= uE

I= qnAv or I= qnAuE

q = charge of electron = -1.6e-19
A = cross sectional area
v= drift speed
u= electron mobility which is = 1.2e-4
n= 6.3e28

3. The attempt at a solution

I have tried every way like used v=uE but therer are two unknowns, then in I= qnAuE there are two unknowns, what do I do.

ONE MORE THINg
When The compass is placed on top of the wire, it deflects by 20 degrees away from North towards the west. But this doesn't help again does it? Does anyone knows how to use the degrees to solve the question or some other way then please distribute your valuable knowledge please help!!!